The invention relates to a new hydrophobic composition for cementitious mortars. Especially, it relates to a cementitious composition that can effectively reduce the adsorption of water.
Redispersible polymer powders have been employed for many years, in particular in the building sector, for modifying hydraulic systems such as cement-based adhesives and dry mixes in order to improve the strength properties. The advantages of using redispersible polymer powders instead of e.g. aqueous polymer dispersions are, inter alia, a high storage stability without addition of preservatives and the frost resistance of the pulverulent dry mixtures. Commercially available redispersible polymeric powders that have been used in e.g. cement-based tile adhesives and self-level flooring compounds include vinyl acetate/ethylene copolymers, various acrylic polymers, styrene/butadiene copolymers, and vinyl acetate/versatic acid vinyl ester copolymers.
Hydrophobic additives are usually used in cementitious mortars to reduce the adsorption of water of the resulting cementitious composition, among them, most commonly developed and used are organosilicon compounds, fatty acids and the fatty acid derivatives thereof, and hydrocarbon waxes. These additives either increase the water demand of the mortar, thus reducing the strength properties or they make the wetting of the mortar very difficult due to their high surface tension. For example, combinations of redispersible polymer powders with hydrophobic agents, like sodium oleate, are found to thicken the modified mortar and have a negative impact on workability.
U.S. Pat. No. 6,268,423 B1 teaches the use of organosilicon compounds as hydrophobicing agents in construction material. However, these materials do not have binding properties and do not contribute to the strength of the cured mortar.
US20030114583A 1 also describes functionalized copolymers hydrophobicized with silicones, in the form of aqueous dispersions or water-redispersible powders.
The present inventors the present invention have surprisingly found that using dioic acids or anhydrides, i.e. alkenyl substituted succinic acids, in combination with redispersible polymer powders will improve significantly the hydrophobicity of the cured mortars. More surprisingly, it is found out that the combination of redispersible polymer powder with dioic acid esters does not impact the water-demand and the rheology of the fresh cementitious composition.